Light emitting diodes (LED) and related light emitting devices are used in a vast number of applications. These can be used in most light emitting devices from simple panel lights to complex displays and lasers. Currently LEDs are used in the automotive industry, consumer instrumentation electronics, and many military applications. Different compounds are used to produce different wavelengths of light. For example, aluminum gallium arsenide is used for red LEDs, gallium aluminum phosphide for green, and GaN for blue. Light emitting materials formed from three different materials are often difficult to produce. Utilizing different LEDs together inherently requires allowing for different performance characteristics such as current and voltage requirements.
Wide band gap semiconductors (WBGS) doped with light emitting elements such as rare earth elements (RE) and other elements with partially filled inner shells are particularly attractive for LEDs because the emission efficiency appears to increase with band gap value, thus allowing room temperature operation without the need to introduce impurities. Wide band gap generally refers to a band gap of 2 eV or greater. Electroluminescence has been reported from several WBGS hosts including Er-doped gallium arsenide, gallium phosphide, GaN, ZnSe and SiC. Er-doped semiconductor light emitting diodes have been shown to emit in the infrared at about 1.5 microns. The infrared emission corresponds to transmissions between the lowest excited state (4I13/2) and the ground state (4I15/2) of the erbium atoms. The first Er-doped semiconductor light emitting diodes emitted IR light only at very low temperatures. However, recent advancements have permitted IR light emission at near room temperature. Although IR emitting Er-doped GaN has a great deal of utility in the communications industry, it previously has not been useful in a light emitting diode requiring visible emission.
The present invention is premised on the realization that wide band gap semiconductor substrates doped with elements with partially filled inner shells such as rare earth elements and transition metals can be formed and will emit in the visible and ultraviolet spectrum at a wide range of temperatures. The wide band gap semiconductor material are group III-V and IV materials including diamond, GaN, AIN, InN, BN and alloys thereof. These are doped with elements such as cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, turbium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium or other elements with partially filled inner shells.
By proper formation of the wide band gap semiconductor material and proper introduction of the rare earth element, a light emitting diode can be formed which emits in the visible spectrum.
By selection of the appropriate dopant material, one can select the appropriate color. For example, in GaN, erbium will produce green whereas thulium will produce blue and praseodymium will produce red.
The objects and advantages of the present invention will be further appreciated in the light of the following detailed description and drawing in which: